1. Field of the Invention
The present invention relates to vehicle transmission overdrive gear arrangements, especially for four wheel drive vehicles.
2. Description of the Prior Art
In the past, several types of transmission overdrive gearing arrangements have been employed. All commercial types of overdrive gear systems have suffered from severe limitations. Some conventional gear arrangements require a separate overdrive gear case assembly which must be interposed in the drive line of an automotive vehicle. This involves longitudinally relocating major transmission or power transfer box assemblies, which in turn necessiates restructuring the frame supports necessary to carry these major gear box and power transfer box assemblies. In one commercially available system, an auxiliary overdrive gear box is provided at the output of the power transfer box, but is connected only to one pair of wheels for a four wheel drive vehicle. As a consequence, the vehicle does not have overdrive capability when operating with all four wheels engaged for four wheel drive operation.
In another conventional device the power transfer block is moved rearward relative to the vehicle transmission so that an auxiliary overdrive gear box can be interposed between the transmission and the power transfer box. This has led to structural defficienies and inadequate mounting support for these major gear arrangements. The power transfer gear box is thereby longitudinally shifted rearward approximately 12 inches, so that new support mounts are necessary. Moreover, with the use of an auxiliary gear box, spacial constraints in the power train mounting, normally very restrictive, are aggravated even further.